The present invention relates generally to charge pump circuits and more particularly to a charge pump circuit for a phase locked loop (PLL).
Charge pump circuits are employed in phase locked loops (PLLs) to tune a voltage-controlled oscillator (VCO) in response to phase error information detected by a phase-frequency detector.
Current mismatch is known to occur in such charge pump circuits when the PLL is in a phase-locked state. The current mismatch creates a skew or phase offset and reference frequency spurs in the output of the PLL. The skew in the output of the PLL is undesirable in synchronous systems as it consumes a portion of the timing margin available to such systems and thus impairs system performance.
Thus, it would be desirable to have a charge pump circuit that is able to reduce current mismatch in a phase-locked state.